1. Field of the Invention
The present invention relates to a method and a device for inspecting bags, and in particular, it relates to an improved method for inspecting whether bottoms of square bottom bags (called "SOS" bags) or hexagonal bottom bags (called "cross bottom bags") are exactly folded or not to detect (reject) defective products, and to a device for carrying out said method.
2. Description of the Related Art
Proposals have been made to inspect whether bottoms of bags are exactly folded or not by a SOS bag machines or hexagonal bottom forming machines (called "a cross bottomer" or simply "a bottomer"). For example, regarding hexagonal bottom bags, Japanese Examined Patent Publication (Kokoku) No. 62-59022 discloses a method for inspecting bags while bags are conveyed on a bottomer after the bottoms thereof are folded and closed. The bodies of the bags are arranged in a flat and horizontal position, and the spreaded or dosed bottoms of the bags are arranged in a vertical position, i.e., perpendicular to the bag bodies. The bottom has a pair of upper and lower opposite sides and four remaining oblique sides. The bags are conveyed in transverse direction, i.e., the upright bottoms are parallel to the conveying direction. The inspecting device comprises four photoelectric cells; two cells are arranged just outside the upper and lower sides to normally emit a bright signal, and the remaining two cells are arranged just inside the upper and lower sides to emit a normally dark signal, so that the top and lower sides of the moving bottoms are scanned and it is judged whether the bottoms are exactly folded or not due to a detected parallelism of the upper and lower sides.
Japanese Unexamined Patent Publication (Kokai) No. 54-126177 also discloses a method for inspecting hexagonal bottom bags. The bags are conveyed on a bottomer in a similar manner to the above described case, so that the bags are conveyed in transverse direction, i.e., the upper and lower sides of the bottoms are parallel to the conveying direction. The inspecting device comprises four photoelectric cells and pulse encoders. According to this prior art, the length of the upper and lower sides of the bottom, the length from the leading end of the moving bottom (i.e. the apex of the leading triangle pocket) to the leading end of the upper and lower sides, and the length from the trailing end of the top and lower sides to the trailing end of the moving bottom (i.e. the apex of the trailing triangle pocket) are measured, and it is judged whether triangular pockets of the bottom are exactly folded at 45 degrees or not.
In addition, this publication also discloses to carry out the detection during a bottom forming process before the bottom of the bag is finally closed, i.e., just after the bottom end is spreaded. In this case too, the length of the top and lower sides of the bottoms, the length from the leading end of the bottom (i.e. the apex of the training triangle pocket) to the leading ends of the upper and lower sides, and the length from the trailing end of the top and lower sides, to the trailing end of the moving bottom (i.e. the apex of the trailing triangle pocket) so as to judge whether triangular pockets of the bottoms are exactly folded at 45 degrees or not.
However, these inspecting methods and devices can be applied only to the hexagonal bottom manufacturing machines in which the bags are conveyed in such a manner that the bottoms are arranged in a vertical position relative to the horizontal flat tube bodies and the bags are conveyed in transverse direction, but cannot be applied to the SOS bag machines in which the bags are conveyed in such a manner that the bags are conveyed in longitudinal direction with the bottoms directed on the leading side, since these inspecting methods and devices use photoelectric cells. That is, the bottom is overlapped with the bag body, so it is difficult to identify the contour of the bottoms with the use of photoelectric cells.
A further device for inspecting so-called SOS bags having square bottoms is shown in FIGS. 5A and 5B, in which detecting rollers 15 are arranged on a delivery cylinder 14 which is arranged in a SOS bag machine after a bottom closing station. Magnetic field type proximity switches 16 are arranged to cooperate with the detecting rollers 15. FIG. 6 shows a SOS bag 20 having a square bottom 21 comprising folded flaps 22 delimited by outer shape lines 23. The detecting rollers 15 are arranged so that they contact the portions A, B, C and D of the bottom 21. The thickness of the portions A, B, C and D of the bottom 21 differs from each other due to the difference in the overlapped paper layers. The proximity switches 16 detect the thickness of the portions A, B, C and D and it is judged whether the bottom 21 of the bag 20 is exactly folded or not by comparing the detected thickness and a predetermined value.
For example, the portions A and B are symmetrically arranged to each other and the portions C and D are symmetrically arranged to each other, with the portion C including a longitudinal seam 24. Accordingly, the portions A and B comprise 6 layers, the portion C comprises 14 layers, and the portion D comprises a 10 layers. If the bottom 21 is not exactly folded and a portion or the whole of the portions A, B, C, and D is shifted out of the detecting rollers 15, the detected thickness will not correspond to the predetermined values and the bag will be rejected by a rejection means.
In this SOS bag machine, there are problems in that an erroneous inspection occurs if the bags are caught not correctly (e.g. aslant) gripped by fingers on the delivery cylinder 14, that an erroneous detection occurs if the detecting rollers 15 jump depending on the urging pressure thereof, and that it is not possible to carry out the detection at positions where fingers or grooves are located on the delivery cylinder 14 and so it is not possible to carry out the inspection for some particular bag sizes.
The above described prior arts inspect whether the bottoms are exactly folded or not by detecting or measuring the position, the dimension or the thickness of a particular portion or portions of the bottoms of the bags, based on the assumption that the folding lines or the outer shape lines of the flaps are straight irrespective of the fact that the bottoms are exactly folded or not. According to these prior arts, an erroneous inspection may occur if the bottom fold lines or the outer shape lines of the flaps are curved or the flaps are wrinkled. Also, it is not possible to detect any break in the flaps which may occur during folding the flaps.